Diagnosing A Bad Idler Pulley, Bad Tensioner Pulley, and More

Diagnosing A Bad Idler Pulley, Bad Tensioner Pulley, and More
August 19, 2021
Diagnosing A Bad Idler Pulley, Bad Tensioner Pulley, and More

Is your car making a loud chirping or screeching noise? It could be a bad pulley. Your car has many different pulley systems: an idler pulley, a tensioner pulley, and a water pump pulley, among others –and any one of these parts can go bad. We’ll tell you how to check for bad pulleys in your car

Checking for a Bad Pulley


All the pulley systems in your vehicle have different functions, but there are common links between them. Whether you’re checking for a bad alternator pulley or a bad tensioner pulley, all these different parts have similar symptoms when they go bad

You Hear a Squealing or Chirping Sound

Hearing sounds like squealing or chattering from your car are the most obvious signs you have a bad belt or loose pulley bearing. The type of sound you hear can be used to diagnose your problem. If you hear a chattering noise, it’s most likely a pulley that’s either too tight or too loose. If it sounds like squealing, your pulley might be seized up and overheating.

You Pulley Has a Corroded Surface

Pulleys can get rusted or rotted, and this degradation causes your serpentine belt to wear out prematurely. Normal pulleys have nice smooth surfaces. If you notice rust on your pulley, depending on the amount of damage to the pulley you can try sandpapering off the decay, or if it’s too severe, completely replace it.

Your Idler Pulley Has Gotten Too Loose

If you suspect your idler pulley has gotten loose, you can test it and look for signs. If it’s gone bad, it’ll make chattering noises while it spins. It’ll also cause vibration, which can knock your serpentine belt off course.

If this part’s gotten loose, it could be because of bad bearings. Be sure to also check for excessive play by wiggling it back and forth. A normal pulley should only move slightly when you wiggle it. If it moves around a lot, you’ll know it needs to be replaced.

Your Idler Pulley Is Spinning Too Much

To test for excessive spinning, spin the pulley yourself. If it’s working normally, it’ll only spin in place a few times. If it has problems with its bearings, it’ll spin much more than that. It might even make strange sounds.

Your Pulley Isn’t Spinning, or it’s Binding Up

While your pulley is spinning, only the outer part should spin; the center should remain in place. When it’s healthy, the part will spin a few times without any resistance, then stop. If you notice binding, then like any other bad part on your car, you’ll have to replace it.

How to Replace a Bad Idler Pulley

Materials Needed to Replace a Bad Idler Pulley

  • A new idler pulley
  • Socket set and ratchet – Sizes vary by make, model, and country of origin so it’s best to have metric and standard handy
  • Torque wrench – It’s important to not over torque any nuts or bolts on your vehicle and the idler pulley bolt is no exception.
  • A breaker bar MAY be necessary to move the alternator
  • Mechanic’s gloves

Step 1: Start by disconnecting the negative battery terminal. You want to make sure there is no charge traveling through the electrical components. This prevents damage to your car and you. Move the cable aside so it cannot make contact with anything metal. If needed, you can wrap it in tape or a plastic bag to prevent making contact.

Step 2: Next we remove the drive belt. You have to relieve the tension on the belt to remove it from the pulleys. For an idler pulley that attaches to your alternator, you will need to remove the bolt attaching the pulley to the alternator. Then push the alternator down to relieve the tension on the belt If the alternator is hard to move there may be a place to insert the breaker bar to give you leverage. If the pulley attaches to your engine block, you need to loosen the pulley bolt from the engine block and push the pulley back to relieve tension on the drive belt.

*DIY Mechanic’s Note*: Might as well replace the drive or serpentine belt since you have it off. That way you know you have two good new components in the system.

Step 3: Now we remove the old pulley. Push the belt out of the way and remove the retaining bolt. Pull the pulley out. New pulleys typically do not come with hardware so keep any gaskets, bolts, and other hardware that come off with the pulley. Install the new pulley using the old hardware in the exact same order. If the old hardware is damaged, it’s best to buy all new hardware but make sure you get the right size replacements.

*DIY Mechanic’s Note*: When removing the pulley (or any parts from your car) lay them out in the order you took them off and replace them in that same order. This ensures that everything goes on the right way and prevents you from having to do it all over again.

Step 4: Let’s install the new pulley. It’s best to compare the new pulley to the old, now. This step just reconfirms that you ordered the correct idler pulley from Partshawk.com. Using the existing hardware from the bad pulley.

*DIY Mechanic’s Note*: Be sure to assemble and install the new pulley and hardware in the order in which laid them out when you took them off. (See previous DIY Mechanic’s Note)

Step 5: Tighten the new pulley. Use the torque wrench to tighten the pulley bolt to the manufacturer’s recommended torque. It’s usually about 40 ft/lb. You just set the wrench to 40 ft/lb. When you hit that torque on the bolt the handle will turn but it will click. This means the required torque was achieved.

Step 6: Place the drive belt back on the pulleys in the same pattern it was removed. If you had to move the alternator or anything to relieve tension on the belt, make sure you move it back into position, once you have placed the belt. This puts tension back on the belt. Without tension, the pulley system will not function.

Step 7: Replace the negative battery cable and tighten the cable bolt

Now start the car up and witness the quiet that is your engine.

*DIY Mechanic’s Note*: If you are just reading the blog before buying the parts to see if you can do it yourself, it’s that time. Visit Partshawk.com and get all the pulley parts you need to fix that screeching idler pulley. Contact us at (650) 560-Hawk if you need help finding any certain parts.

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